kees de jager jefferson lab nuclat april 21 - 22, 2008
DESCRIPTION
Nucleon Electro-Weak Form Factors. g. Z 0. General Introduction Electromagnetic Form Factors Formalism Neutron Proton Parity Violation Formalism Strange Form Factors Summary. Kees de Jager Jefferson Lab NUCLAT April 21 - 22, 2008. Thomas Jefferson National Accelerator Facility. - PowerPoint PPT PresentationTRANSCRIPT
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NUCLAT, April 21-22, 2008, 1
Kees de JagerJefferson LabNUCLATApril 21 - 22, 2008
Nucleon Electro-Weak Form Factors
•General Introduction•Electromagnetic Form Factors
•Formalism•Neutron•Proton
•Parity Violation•Formalism•Strange Form Factors
•Summary
Thomas Jefferson National Accelerator Facility
Z0
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NUCLAT, April 21-22, 2008, 2
(Hadronic) Structure and (EW) Interaction
StructureInteraction
Probe Object
|Form factor|2 =
Electroweak probe
Interaction
Structure
(structured object)
(pointlike object)
Hadronic object
→ Interference!
Factorization!
Lepton scattering
→ Utilize spin dependence of electroweak interaction to achieve high precision
Inelastic Elastic
Born Approximation
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NUCLAT, April 21-22, 2008, 3
Kinematics
→ Q2 > 0 space-like region, studied through elastic electron scattering
→ Q2 < 0 time-like region, studied through creation or annihilation
e+ + e- -> N + N or N + N -> e+ + e-
_ _
rq =
rp−
rp'
ω =Ee − ′Ee
−Q2 ≡t≡q2 =ω 2 −rq2
Q2 ≈4EE'sin2θe / 2
J μ =U(P') μF1(Q2 ) +
i μνqv
2M p
κF2 (Q2 )
⎧⎨⎪
⎩⎪
⎫⎬⎪
⎭⎪U(P)
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NUCLAT, April 21-22, 2008, 4
Nucleon Electro-Magnetic Form Factors
Fundamental ingredients in “Classical” nuclear theory
• A testing ground for theories constructing nucleons from quarks and gluons
• Provides insight in spatial distribution of charge and magnetization
• Wavelength of probe can be tuned by selecting momentum transfer Q:
< 0.1 GeV2 integral quantities (charge radius,…)
0.1-10 GeV2 internal structure of nucleon
> 20 GeV2 pQCD scaling
Caveat: If Q is several times the nucleon mass (~Compton wavelength), dynamical effects due to relativistic boosts are introduced, making physical interpretation more difficult
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NUCLAT, April 21-22, 2008, 5
Formalism
€
dσdΩ
(E,θ) =α 2E 'cos2 (
θ
2)
4E 3 sin4 (θ
2)
[(F12 +κ 2τ F2
2) + 2τ (F1 +κF2)2 tan2 (
θ2
)]
Dirac (non-spin-flip) F1 and Pauli (spin-flip) F2 Form Factors
with E (E’) incoming (outgoing) energy, θ scattering angle, κ anomalous magnetic moment and = Q2/4M2
In the Breit (centre-of mass) frame the Sachs FF can be written as the Fourier transforms of the charge and magnetization radial density distributions
ddΩ
(E,θ) =M [GE
2 +GM2
1++ 2GM
2 tan2 (θ2)]
M =α 2E 'cos2 (
θ
2)
4E 3 sin4 (θ
2)
F1 =GE +GM F2 =GM −GE
κ(1+ ) =
Q2
4M 2
Alternatively, Sachs Form Factors GE and GM can be used
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NUCLAT, April 21-22, 2008, 6
The Pre-JLab Era
• Stern (1932) measured the proton magnetic moment µp ~ 2.5 µDirac
indicating that the proton was not a point-like particle• Hofstadter (1950’s) provided the first measurement of the
proton’s radius through elastic electron scattering• Subsequent data (≤ 1993) were based on:
Rosenbluth separation for proton, severely limiting the accuracy for GE
p at Q2 > 1 GeV2
• Early interpretation based on Vector-Meson Dominance
• Good description with phenomenological dipole form factor:
€
GD =Λ2
Λ2 + Q2
⎧ ⎨ ⎩
⎫ ⎬ ⎭
2
with Λ = 0.84GeV
corresponding to (770 MeV) and ω (782 MeV) meson resonances in timelike region and to exponential distribution in coordinate space
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NUCLAT, April 21-22, 2008, 7
Global Analysis (1995)
P. Bosted et al. PRC 51, 409 (1995)
Three form factors very similar
GEn zero within errors ->
accurate data on GEn early goal
of JLab
GEp / GD =GM
p /GD = 1+ aiQi
i=1
5
∑⎛⎝⎜
⎞⎠⎟;
GMn /GD = 1+ biQ
i
i=1
4
∑⎛⎝⎜
⎞⎠⎟; GE
n =0
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NUCLAT, April 21-22, 2008, 8
Modern Era
Akhiezer et al., Sov. Phys. JETP 6, 588 (1958) andArnold, Carlson and Gross, PR C 23, 363 (1981) showed that:
accuracy of form-factor measurements can be significantly improved by measuring an interference term GEGM through the beam-helicity asymmetry with a polarized target or with recoil polarimetry
Had to wait over 30 years for development of
• Polarized beam with high intensity (~100 µA) and high polarization (>70 %)
(strained or superlattice GaAs, high-power diode/Ti-Sapphire lasers)
• Beam polarimeters with 1-3 % absolute accuracy• Polarized targets with a high polarization or• Ejectile polarimeters with large analyzing powers
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NUCLAT, April 21-22, 2008, 9
Double Polarization Experiments to Measure GnE
€
GEn
GMn =
A⊥
A||
τ +τ (1+ τ )tan2 (θ2
)
• Study the (e,e’n) reaction from a polarized ND3 targetlimitations: low current (~80 nA) on target
deuteron polarization (~25 %)
• Study the (e,e’n) reaction from a LD2 target and measure the neutron polarization with a polarimeter limitations: Figure of Merit of polarimeter
• Study the (e,e’n) reaction from a polarized 3He targetlimitations: current on target (12 µA)
target polarization (40 %)nuclear medium corrections
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NUCLAT, April 21-22, 2008, 10
GnE Experiment with Neutron Polarimeter
€
ξ ∝ sin χ +δ( )⇒GE
n
GMn = −tanδ
τ 1 +ε( )
2ε
• Use dipole to precess neutron spin• Up-down asymmetry ξ
proportional to neutron sideways polarization
• GE/GM depends on phase shift w.r.t. precession angle
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NUCLAT, April 21-22, 2008, 11
Neutron Electric Form Factor GEn
Galster: a parametrization fitted to old (<1971) data set of very limited quality
For Q2 > 1 GeV2 data hint that GE
n has similar Q2-behaviour as GE
p
Most recent results (Mainz, JLab) are in excellent agreement, even though all three different techniques were used
GEn (Q2 ) =
−μnQ2
4Mn2 +bQ2( )
GD Q2( )
Schiavilla and Sick analyzed data on deuteron elastic quadrupole form factor
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NUCLAT, April 21-22, 2008, 12
Exclusive QE scattering: 3He(e,e′n)
e′
n
2 veto planes
7 Iron/scintillatorsandwich planes
e
Beam polarization
84%
Target polarization
~50%
Q2 = 1.3, 1.7, 2.5, 3.5 GeV2
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NUCLAT, April 21-22, 2008, 13
First physics result from Hall A GEn
1.7 GeV2 datum is well above Galster Nuclear corrections include neutron polarization and FSI estimate (5%) Present error (∼20%) dominated by preliminary “neutron dilution factor”, and is expected to be ∼7% stat. and 8% syst. with further analysis 3.4 GeV2 datum, however, is on top of Galster
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NUCLAT, April 21-22, 2008, 14
Measuring GnM
•Measure (en)/(ep) ratioLuminosities cancelDetermine neutron detector efficiency
•On-line through e+p->e’+π+(+n) reaction (CLAS)•Off-line with neutron beam (Mainz)
€
RD =
d3σ (eD ⇒ e 'n(p))
dE ' dΩe 'dΩn
d3σ (eD ⇒ e ' p(n))
dE 'dΩ e'dΩ p
Old method: quasi-elastic scattering from 2Hlarge systematic errors due to subtraction of proton contribution
€
A =− cosθ *vT 'RT ' + 2sinθ *cosϕ *vTL'RTL'( )
vLRL + vTRT
RT’ directly sensitive to (GMn)2
• Measure inclusive quasi-elastic scattering off polarized 3He
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NUCLAT, April 21-22, 2008, 15
Measurement of GnM at low Q2
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NUCLAT, April 21-22, 2008, 16
Preliminary CLAS results for GMn
A systematic difference of several % between results ( ) in Q2 range 0.4 - 0.8 GeV2. A final analysis and paper from CLAS is coming soon.Reminder that at least two independent experiments are always needed.
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NUCLAT, April 21-22, 2008, 17
Early Measurements of GEp
•relied on Rosenbluth separation•measure d/dΩ at constant Q2
•GEp inversely weighted with Q2, increasing the systematic error
above Q2 ~ 1 GeV2
€
Q2 = 4EE 'sin2(θ2
)
At 6 GeV2 R changes by only 8% from =0 to =1 if GE
p=GMp/µp
Hence, measurement of GEp
with 10% accuracy requires 1.6% cross-section measurement
=1
1+ 2(1+ τ ) tan2 (θ / 2)
R Q2 ,ε( ) = ε 1+1
τ⎛⎝⎜
⎞⎠⎟
E
E '
σ E,θ( )
σ Mott
= (GMp )2 Q2( ) +
ε
τ(GE
p )2 Q2( )
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NUCLAT, April 21-22, 2008, 18
Spin Transfer Reaction 1H(e,e’p)
€
r
€
r
€
Pn = 0
±hPt = mh2 τ (1+ τ )GEpGM
p tanθe
2
⎛ ⎝
⎞ ⎠/ I0
±hPl = ±h Ee + Ee'( ) GMp
( )2
τ (1+ τ )tan2 θe
2
⎛ ⎝
⎞ ⎠/ M / I0
I0 = GEp Q2( ){ }
2+ τ GM
p Q2( ){ }
21+ 2(1+ τ )tan2 θ e
2
⎛ ⎝
⎞ ⎠
⎡
⎣ ⎢ ⎤
⎦ ⎥
€
GEp
GMp = −
Pt
Pl
Ee + Ee'
2Mtan
θ e
2
⎛ ⎝
⎞ ⎠
No error contributions from• analyzing power• beam polarimetry
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NUCLAT, April 21-22, 2008, 19
Recoil Polarization Measurement
Observed angular distribution
Focal-Plane Polarimeter
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NUCLAT, April 21-22, 2008, 20
JLab Polarization Transfer Data
•E93-027 PRL 84, 1398 (2000)Used both HRS in Hall A with FPP
•E99-007 PRL 88, 092301 (2002)used Pb-glass calorimeter for electron detection to match proton HRS acceptance
•Reanalysis of E93-027 (Punjabi, nucl-ex/0501018)Using corrected HRS properties
•No dependence of polarization transfer on any of the kinematic variables
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NUCLAT, April 21-22, 2008, 21
Super-Rosenbluth (E01-001)
I. Qattan et al. (PRL 94, 142301 (2005))• Detect recoil protons in HRS-L to diminish
sensitivity to:• Particle momentum• Particle angle• Rate
• Use HRS-R as luminosity monitor• Very careful survey
RosenbluthPol TransMC simulations
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NUCLAT, April 21-22, 2008, 22
Rosenbluth Compared to Polarization Transfer
• John Arrington performed detailed reanalysis of SLAC data• Hall C Rosenbluth data (PRC 70, 015206 (2004)) in agreement with
SLAC data• No reason to doubt quality of either Rosenbluth or polarization transfer
data• Investigate possible theoretical sources for discrepancy
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NUCLAT, April 21-22, 2008, 23
Two-Photon Exchange Proton form factor measurements
• Comparison of precise Rosenbluth and polarization measurements of GEp/GMp show clear discrepancy at high Q2
Two-photon exchange corrections believed to explain the discrepancy
Compatible with e+/e- ?• Yes: previous data limited to
low Q2 or small scattering angle
Still lack direct evidence of effect on cross section• Transverse single spin
asymmetry is the only observable in elastic e-p where TPE observed
P.A.M.Guichon and M.Vanderhaeghen, PRL 91, 142303 (2003)
Chen et al., PRL 93, 122301 (2004)
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NUCLAT, April 21-22, 2008, 24
24
Two-Photon Exchange Measurements
Comparisons of e+-p and e--p scattering [VEPP-III, JLab-Hall B, BLAST@DORIS]
ε dependence of polarization transfer and unpolarized σe-p [JLab-Hall C]
• More quantitative measure of the discrepancy• Test against models of TPE at both low and high Q2
TPE effects in Born-forbidden observables [JLab-Hall A, Hall C, Mainz]
• Target single spin asymmetry Ay in e-n scattering
• Induced polarization py in e-p scattering
• Vector analyzing power AN in e-p scattering
World’s dataNovosibirskJLab – Hall B
Evidence (3 level) for TPE in existing data
J. Arrington, PRC 69, 032201(R) (2004)
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NUCLAT, April 21-22, 2008, 25
Two-Photon Exchange Calculations Significant progress in theoretical understanding
• Hadronic calculations appear sufficient up to 2-3 GeV2
• GPD-based calculations used at higher Q2
Experimental program will quantify TPE for several e-p observables
Before TPEAfter TPE (Blunden, et al)
• Precise test of calculations
• Tests against different observables
Want calculations well tested for elastic e-p, reliable enough to be used for other reactions
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NUCLAT, April 21-22, 2008, 26
Reanalysis of SLAC data on GM
p
E. Brash et al. (PRC 65, 051001 (2002)) have reanalyzed SLAC data with JLab GE
p/GMp results
as constraint, using a similar fit function as BostedReanalysis results in 1.5-3% increase of GM
p data
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NUCLAT, April 21-22, 2008, 27
Charge and Magnetization Radii
€
r2 ≡ 4π ρ (r)r4 dr = −6
G(0)dG(Q2)
dQ2∫Experimental values<rE
2>p1/2= 0.895+0.018 fm
<rM2>p
1/2= 0.855+0.035 fm<rE
2>n= -0.119+0.003 fm2
<rM2>n
1/2= 0.87+0.01 fm
€
dGEn (Q2)
dQ2 Q 2= 0=
dF1n (Q2)
dQ2 Q 2= 0−
F2n(0)
4M 2
Foldy term = -0.126 fm2 canceled by relativistic corrections (Isgur)implying neutron charge distribution is determined by GE
n
Even at low Q2-values Coulomb distortion effects have to be taken into accountThe three real radii are identical within the experimental accuracy
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NUCLAT, April 21-22, 2008, 28
Low Q2 Systematics
All EMFF show minimum (maximum for GEn) at Q ≈ 0.5 GeV
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NUCLAT, April 21-22, 2008, 29
Pion Cloud
•Kelly has performed simultaneous fit to all four EMFF in coordinate space using Laguerre-Gaussian expansion and first-order approximation for Lorentz contraction of local Breit frame
€
˜ G E,M (k) = GE ,M (Q2) 1+ τ( )2 with k 2 =
Q2
1+ τ and τ =
Q
2M
⎛ ⎝
⎞ ⎠
2
• Friedrich and Walcher have performed a similar analysis using a sum of dipole FF for valence quarks but neglecting the Lorentz contraction
• Both observe a structure in the proton and neutron densities at ~0.9 fm which they assign to a pion cloud
• Hammer et al. have extracted the pion cloud assigned to the NN2π component which they find to peak at ~ 0.4 fm
_
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NUCLAT, April 21-22, 2008, 30
New Polarization Transfer Results for GEp
• Parasitic to G0
• 40% Polarized Beam• Approx. 12 hours/point
Cross Section from C. Berger et al., Phys. Lett. B35 (1971) 87Deviation in Ratio is due to Electric Form Factor
PRL 99, 202002 (2007)
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NUCLAT, April 21-22, 2008, 31
Approved Experiment E04-007
One Day of Beam Time per Point!Will run in May/June 2008
Extensive program of accurate cross-section measurements at low Q2 ongoing at MAMI
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NUCLAT, April 21-22, 2008, 32
High-Q2 behaviour
Basic pQCD (Bjørken) scaling predicts F1 1/Q4 ; F2 1/Q6
F2/F1 1/Q2 (Brodsky & Farrar)Data clearly do not follow this trend
Schlumpf (1994), Miller (1996) andRalston (2002) agree that by• freeing the pT=0 pQCD condition• applying a (Melosh) transformation to
a relativistic (light-front) system• an orbital angular momentum
component is introduced in the proton wf (giving up helicity conservation) and one obtains
F2/F1 1/Q• and equivalently a linear drop off of
GE/GM with Q2
Brodsky argues that in pQCD limit non-zero OAM contributes to both F1 and F2
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NUCLAT, April 21-22, 2008, 33
High-Q2 BehaviourBelitsky et al. have included logarithmic corrections in pQCD limit
They warn that the observed scaling could very well be precocious
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NUCLAT, April 21-22, 2008, 34
Theory
• Relativistic Constituent Quark ModelsVariety of q-q potentials (harmonic oscillator, hypercentral, linear)Non-relativistic treatment of quark dynamics, relativistic EM currents
• Miller: extension of cloudy bag model, light-front kinematicswave function and pion cloud adjusted to static parameters
• Cardarelli & SimulaIsgur-Capstick oge potential, light-front kinematicsconstituent quark FF in agreement with DIS data
• Wagenbrunn & Plessaspoint-form spectator approximationlinear confinement potential, Goldstone-boson exchange
• Giannini et al.gluon-gluon interaction in hypercentral modelboost to Breit frame
• Metsch et al.solve Bethe-Salpeter equation, linear confinement potential
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NUCLAT, April 21-22, 2008, 35
Relativistic Constituent Quark
charge magnetization
proton
neutron
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NUCLAT, April 21-22, 2008, 36
Time-Like Region
•Can be probed through e+e- -> NN or inverse reaction_
•Data quality insufficient to separate charge and magnetization contributions•No scaling observed with dipole form factor•Iachello only model in reasonable agreement with data•Large new accurate data set from BaBar/ CLEO /DANE
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NUCLAT, April 21-22, 2008, 37
In the simple valence-quark model a nucleon consists of u and d quarks.
Valence and Sea Quarks in the Nucleon
However, ss pairs are continuously created and annihilated and are known to contribute to a variety of nucleon properties, such as mass (0-30%), momentum (2-4%) and spin (0-20%).
Just as pions can cause the zero-charge neutron to have a non-zero charge distribution, the strange sea is expected to contribute to the charge and magnetic moment distribution of nucleons.
but how much?
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NUCLAT, April 21-22, 2008, 38
Elastic Electroweak Scattering
GEs(Q2), GM
s(Q2)
p
AMEF AAAQGA
πα++
⎥⎦
⎤⎢⎣
⎡−=
24
2
APV for elastic e-p scattering:
Forward angle Backward angle
( ) eA
pMWA
ZM
pMM
ZE
pEE GGAGGAGGA '2sin41 , , εθτε −−===
Helium: unique GE sensitivityDeuterium: enhanced GA sensitivity
Z0
Kaplan & Manohar (1988)McKeown (1989)
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Flavor Separation of Nucleon Form Factors
•If we can measure
with
:,, ,,, npZp GGG
( )psME
pdME
puME
pME GGGG ,
,,,
,,
,, 3
1
3
2+−=γ
nsps
nupd
ndpu
GG
GG
GG
,,
,,
,,
=
=
=
dropping the p superscripts on the left
then we can write
by assuming charge symmetry
G ~ N eii∑ qiΓμqi N
GE ,Mu =(3−4sin2θW )GE,M
,p −GE,MZ,p
GE,Md =(2 −4sin2θW )GE,M
,p +GE,M,n −GE,M
Z,p
GE,Ms =(1−4sin2θW )GE,M
,p −GE,M,n −GE,M
Z,p
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Instrumentation for PVES
Large -Acceptance Detectors (G0, A4) Large kinematic range Poor background suppression
Spectrometer (HAPPEx) Good background rejection Scatter from magnetized iron
Cumulative Beam Asymmetry• Helicity-correlated asymmetryx~10 nm, I/I~1 ppm, E/E~100 ppb
Helicity flips• Pockels cell• half-wave plate flips
!!!1010 1413 −≈N
%52
11==
NAAA
610−−+
−+
≈+−
=
PVA
Need• Highest possible luminosity• High rate capability• High beam polarization
Detectors Integrating (HAPPEx) vs. Counting (G0, A4)
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NUCLAT, April 21-22, 2008, 41
Overview of Experiments
GMs, (GA) at Q2 = 0.1 GeV2
SAMPLE
HAPPEx GEs + 0.39 GM
s at Q2 = 0.48 GeV2
GEs + 0.08 GM
s at Q2 = 0.1 GeV2
GEs at Q2 = 0.1 GeV2 (4He)
open geometry, integrating
A4
GEs + 0.23 GM
s at Q2 = 0.23 GeV2
GEs + 0.10 GM
s at Q2 = 0.1 GeV2
GMs, GA
e at Q2 = 0.1, 0.23, 0.5 GeV2
open geometry
fast-counting calorimeter for background rejection
Electron Beam
LH2 Target
SuperconductingCoils
Particle Detectors
G0
GEs + GM
s over Q2 = [0.12,1.0] GeV2
GMs, GA
e at Q2 = 0.23, 0.62 GeV2
open geometry
fast-counting with magnetic spectrometer + TOF for background rejection
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Experimental Technique
Compton1.5-3% syst
Continuous
Møller2-3% syst
Polarimeters
High Resolution SpectrometerS+QQDQ 5 mstr over 4o-8o
Target400 W transverse flow20 cm, LH220 cm, 200 psi 4He
Cherenkovcones
PMT
PMTElastic Rate:1H: 120 MHz4He: 12 MHz
100 x 600 mm
12 m dispersion
sweeps away inelastic events
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New HAPPEx Results
Asym
metr
y
(pp
m)
Slug
Hydrogen
Araw correction ~11 ppb
Slug
Asym
metr
y
(pp
m)
Helium
normalization error ~ 2.5%
APV = -1.58 0.12 (stat) 0.04 (syst) ppmA(Gs=0) = -1.66 ppm 0.05 ppm
HydrogenSystematic control ~ 10-8
APV = +6.40 0.23 (stat) 0.12 (syst) ppmA(Gs=0) = +6.37 ppm
HeliumNormalization control ~ 2%
Helicity Window Pair Asymmetry
Hydrogen
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World Data near Q2 ~0.1 GeV2
Caution: the combined fit is approximate. Correlated errors and assumptions not taken into account
GMs = 0.28 ± 0.20
GEs = -0.006 ± 0.016
~3% ± 2.3% of proton magnetic moment
~0.2 ± 0.5% of Electric distribution
HAPPEX only fit suggests something even smaller:
GMs = 0.12 ± 0.24
GEs = -0.002 ± 0.017
PRL 98, 032301 (2007)
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New data confront theoretical predictions
16. Skyrme Model - N.W. Park and H. Weigel, Nucl. Phys. A 451, 453 (1992).
17. Dispersion Relation - H.W. Hammer, U.G. Meissner, D. Drechsel, Phys. Lett. B 367, 323 (1996).
18. Dispersion Relation - H.-W. Hammer and Ramsey-Musolf, Phys. Rev. C 60, 045204 (1999).
19. Chiral Quark Soliton Model - A. Sliva et al., Phys. Rev. D 65, 014015 (2001).
20. Perturbative Chiral Quark Model - V. Lyubovitskij et al., Phys. Rev. C 66, 055204 (2002).
21. Lattice - R. Lewis et al., Phys. Rev. D 67, 013003 (2003).
22. Lattice + charge symmetry -Leinweber et al, Phys. Rev. Lett. 94, 212001 (2005) & hep-lat/0601025
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Summary and Outlook
• Suggested large values at Q2~0.1 GeV2
• Ruled out
• Possible large values at Q2=0.6 GeV2
• G0 back angle, data being analyzed• HAPPEX-III - 2009
• Large possible cancellation at Q2~0.2 GeV2
• Very unlikely given constraint at 0.1 GeV2
• G0 back angle at low Q2 (error bar~1.5% of μp) maintains sensitivity to discover GM
S0.6 GeV2
G0 backward
HAPPEX-III
GMs
GEs
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Outstanding Precision for Strange Form Factors
This has recently been shown to enable a dramaticimprovement in precision in testing the Standard Model
Q2=0.1 GeV2
Ciq denote the V/A electron-quark coupling constants
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Summary• Very active experimental program on nucleon electro-weak form factors
thanks to development of polarized beam (> 100 µA, > 75 %) with extremely small helicity-correlated properties, polarized targets and polarimeters with large analyzing powers
• Electromagnetic Form Factors• GE
p discrepancy between Rosenbluth and polarization transfer not an experimental problem, but highly likely caused by TPE effects
• GEn precise data up to Q2 = 3.5 GeV2
• GMn precise data up to Q2 = 5 GeV2, closely following
dipole behaviour, but with experimental discrepancies at ~ 1 GeV2
• Further accurate data will continue to become available as benchmark for Lattice QCD calculations
• Parity-violating asymmetries have provided highly accurate data on strange form factors at ~ 0.1 GeV2 with further data in the near future
• Significant advances in measurement of transverse SSAs• Sensitive test of TPE calculations
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Extensions with JLab 12 GeV Upgrade
. BLUE = CDR or PAC30 approved, GREEN = new ideas under development~10 GeV2
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Acknowledgements
Many thanks to the colleagues who willingly provided me with figures/slides/discussions:
• John Arrington• Roger Carlini• Doug Higinbotham• Michael Kohl• Paul Souder• Bogdan Wojtsekhowski